Question

I’ve tried checking for an occurrence of a substring in an NSString in two ways, both have crashed. This is an NSString object I get from one of my NSManagedObject’s properties.

1. Using NSRange

   NSString *searchString = @"drive";

   NSRange range = [text rangeOfString:searchString options:(NSCaseInsensitiveSearch)];

   if (range.location != NSNotFound) {
NSLog(@"Found");
}

2. Using NSScanner

   NSScanner *scanner = [NSScanner scannerWithString:text];

   NSLog(@"%d",[scanner scanString:searchString intoString:nil]);

Both of these work when text = @”drive” but cause EXC_BAD_ACCESS crashes when the text is “i drive”, or “drive to”. Nothing happens if the text is “idrive” or “driveto”.

Even stranger, sometimes the examples throw NSInvalidArgumentExceptions, saying that I tried to pass an NSCFSet or a DateComponents object to rangeOfString:, neither of which I use in my app.

Any ideas?

Answer 1

If you sometimes get EXC_BAD_ACCESS and sometimes get the message “object-of-type-you-weren’t expecting does not respond to method” the chances are you are not retaining the object for long enough and it is getting deallocated before you get to where you use it.

If the memory hasn’t been reused when you get there, things will appear to work. If the space has been reused for another object and aligns perfectly i.e. same pointer, you’ll get something like “x does not respond to selector”. If it’s overwritten in such a way that the pointer does not point to a valid object, you’ll get EXC_BAD_ACCESS